PROJECT SUMMARY It is estimated that scleroderma affects about 300,000 Americans, predominantly women. It is a progressive and untreatable disease of unknown cause and high mortality. No therapy to date has been shown to significantly alter survival but only alleviate the pain. The pathogenesis of scleroderma is characterized by overt inflammation followed by progressive tissue damage and fibrosis secondary to excessive production of collagen and accumulation of myofibroblasts in lesional tissues causing organ failure. Recent genomic studies have revealed potential pathogenic role of inflammatory myeloid cells, including inflammatory monocytes (?IMs) and macrophages (M?s). We have shown for the first time accumulation of MARCO+ ?IMs and M?s within the lesional skin and lung of scleroderma patients and mice with bleomycin-induced scleroderma. MARCO is a type II glycoprotein scavenger receptor expressed by activated phagocytic antigen presenting cells, and is linked to alternate (M2) activation of M?s, resulting in pro-fibrotic activities. The function and pathological contribution of MARCO+ ?IMs and M?s and the therapeutic potential of targeting these cells in scleroderma have never been addressed. We pioneered an innovative strategy targeting ?IMs and M?s by leveraging the drug-like biological properties of carboxylated poly(lactic-co-glycolic acid) (PLGA) nanoparticles. We showed that negatively-charged 500 nM diameter PLGA particles are selectively recognized and bound by ?IMs and M?s via MARCO. PLGA-associated ?IMs/M?s undergo sequestration in the spleen and apoptosis, culminating in reduced immune pathology in bleomycin-treated mice. We hypothesize that PLGA nanoparticle can be used i) as a unique biological probe for illuminating the pathogenic roles of ?IMs and M?s in scleroderma, and to ii) treat inflammation-driven fibrotic diseases. We will test this hypothesis in 3 aims: Aim 1 will measure MARCO levels to determine their clinical significance using skin biopsies from scleroderma patients and healthy controls. Aim 2 will evaluate the efficacy of MARCO-targeting PLGA nanoparticle treatment on progression and alleviation of fibrosis formation in the bleomycin murine model of scleroderma. Aim 3 will delineate mechanisms underlying the deregulated fibrogenic nature of MARCO+ ?IMs and M?s in vitro. In summary, this application leverages exciting preliminary findings from the Miller and Varga labs implicating a pathologic role for MARCO+ ?IMs and M?s in the pathogenesis of scleroderma and showing the potential ability to regulate their pro-fibrotic function using a cutting-edge and translationally-relevant nanoparticle approach. These studies under the co-direction of two well-established PIs benefit from their complementary expertise in inflammation, fibrosis and scleroderma research. The results should significantly advance our understanding of scleroderma by illuminating the pro-fibrotic mechanism(s) of action of MARCO+ ?IMs and M?s, validating the feasibility of a novel therapeutic in preclinical scleroderma models, developing strategies for the identification of patients suitable for the MARCO-targeting therapy.